Peter L. Spence

Postlaunch radiometric validation of the Clouds and the Earth's Radiant Energy System (CERES) Proto-Flight Model on the Tropical Rainfall Measuring Mission (TRMM) Spacecraft through 1999

Abstract Each Clouds and the Earth’s Radiant Energy System (CERES) instrument contains three scanning thermistor bolometer radiometric channels. These channels measure broadband radiances in the shortwave (0.3–5.0 μm), total (0.3–>100 μm), and water vapor window regions (8–12 μm). Ground-based radiometric calibrations of the CERES flight models were conducted by TRW Inc.’s Space and Electronics Group of Redondo Beach, California. On-orbit calibration and vicarious validation studies have demonstrated radiometric stability, defined as long-term repeatability when measuring a constant source, at better than 0.2% for the first 18 months of science data collection. This level exceeds by 2.5 to 5 times the prelaunch radiometric performance goals that were set at the 0.5% level for terrestrial energy flows and 1.0% for solar energy flows by the CERES Science Team. The current effort describes the radiometric performance of the CERES Proto-Flight Model on the Tropical Rainfall Measuring Mission spacecraft over t...

Validation of Geolocation of Measurements of the Clouds and the Earth’s Radiant Energy System (CERES) Scanning Radiometers aboard Three Spacecraft

Abstract The Clouds and the Earth’s Radiant Energy System (CERES) instrument is a scanning radiometer for measuring Earth-emitted and -reflected solar radiation to understand Earth’s energy balance. One CERES instrument was placed into orbit aboard the Tropical Rainfall Measuring Mission (TRMM) in 1997; two were aboard the Terra spacecraft, launched in 1999; and two were aboard the Aqua spacecraft, launched in 2002. These measurements are used together with data from higher-resolution instruments to generate a number of data products. The nominal footprint size of the pixel at Earth’s surface is 16 km in the cross-scan direction and 23 km in the scan direction for the TRMM platform and 36 km in the cross-scan direction and 46 km in the scan direction for the Terra and Aqua platforms. It is required that the location on Earth of each pixel be known to 1–2 km to use the CERES data with the higher-resolution instruments on a pixel basis. A technique has been developed to validate the computed geolocation of ...

In-flight stability analyses applied to the Clouds and the Earth's Radiant Energy System scanning thermistor bolometer instruments on the Terra satellite

Clouds and the Earths Radiant Energy System (CERES) is an investigation into the role of clouds and radiation in the Earths climate system. Two CERES scanning thermistor bolometer instruments are aboard the Earth Observing System (EOS) Terra satellite that was launched 18 December 1999. Each CERES instrument has three sensors that measure in distinct broadband radiometric regions: the shortwave channel (0.3 - 5.0 μm), total channel (0.3 - greater than 100 μm), and window channel (8 - 12 μm). Two analyses have been implemented to aid in monitoring the stability of the measurements of the instruments. One analysis is a three-channel inter-comparison of the radiometric measurements for each instrument. This procedure derives an estimate of the shortwave portion of the total channel sensor radiance measurement. The second analysis is a direct comparison of temporally synchronized nadir measurements for each sensor of the two instruments. Use of these analyses indicates that the shortwave region of the measurements is drifting over mission lifetime for both instruments. A discussion of correcting the shortwave drift using ground software is included.

A comprehensive radiometric validation protocol for CERES Earth Radiation Budget climate record senors

The CERES Flight Models 1 through 4 instruments were launched aboard NASA’s Earth Observing System (EOS) Terra and Aqua Spacecraft into 705 Km sun-synchronous orbits with 10:30 a.m. and 1:30 p.m. equatorial crossing times. These instruments supplement measurements made by the CERES Proto Flight Model (PFM) instrument launched aboard NASA’s Tropical Rainfall Measuring Mission (TRMM) spacecraft on November 27, 1997 into a 350 Km, 38-degree mid-inclined orbit. An important aspect of the EOS program is the rapid archival and dissemination of datasets measured by EOS instruments to the scientific community. Six months after the commencement of science measurements, CERES is committed to archiving the Edition 1 Level 1 instrument, and Level 2 ERBE-Like data products. These products consist of geolocated and calibrated instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA fluxes. CERES filtered radiance measurements cover three spectral bands including shortwave (0.3 to 5 μm), total (0.3 to <100 μm) and an atmospheric window channel (8 to 12 μm). The current work summarizes both the philosophy and results of a validation protocol designed to rigorously quantify the quality of the data products as well as the level of agreement between the TRMM, Terra and Aqua datasets.

Determination and validation of slow mode coefficients of the Clouds and the Earth's Radiant Energy System (CERES) scanning thermistor bolometers

The Clouds and the Earth’s Radiant Energy System (CERES) scanning thermistor bolometers have a response time of approximately 9 ms for 98 to 99% of the signal, after which there is a slow change for the remaining 1 to 2% of the response due to a slow mode. This paper describes the theoretical and experimental procedures used in producing the slow mode coefficients for the CERES Flight Models 1 and 2 instruments aboard the Terra spacecraft, which was launched on December 18,1999. The response behavior for the total thermistor bolometer (0.3 - > 100 µm) and window channel (8-12 µm) were determined by analyzing the internal blackbody calibration ground data while the shortwave thermistor bolometer (0.3 - 5 µm) was determined using shortwave internal calibration source ground data obtained at the TRW calibration facility at Redondo Beach, California. These slow mode coefficients agree with the coefficients obtained by analyzing the in-flight calibration data. A numerical filter removes the effects of the slow mode from the measurements. The method may be applicable to other instruments which have spurious transients.

Geolocation validation of CERES instruments using radiance measurements

Clouds and the Earths Radiant Energy System (CERES) instruments are currently flying on two satellite platforms, Terra, launched 18 December 1999 and Aqua, launched 04 May 2002. Both satellites are at a 705-km altitude, in high inclination, polar orbits. Terra crosses the equator at local morning, while Aqua crosses at local afternoon. Each platform carries two CERES instruments. Each CERES instrument contains three scanning radiation-detecting bolometers. The three detectors measure reflected solar and Earth emitted radiation in three bandwidths: shortwave (0.3-5 μm), window (8-12 μm), and total (0.3 to >100 μm). Earth views of each instrument are geolocated to the Earth fixed coordinate system using satellite attitude, ephemeris, and instrument pointing data. An analysis has been developed which uses radiation gradients at ocean-land boundaries measured by the CERES instrument as an aid to validate the computed geolocation. The detected coastlines are compared to known map coordinates and an error analysis is performed after a best fit is made in the coastline comparison. Spatial differences are mapped from latitude, longitude to absolute distance in along-track (ground path) and cross-track (perpendicular to ground path) of the satellite. Results of the Terra CERES instruments have shown maximum errors to be within 10% of the nadir footprint size. A description of the coastline detection and error analysis will be presented along with results for the Terra CERES instruments. Initial results from the coastline detection and error analysis for the Aqua instruments will be presented also.

Lessons Learned in CERES: Integrating Multiple Instruments on Multiple Platforms with Multiple Sources of Data

This paper discussed the complex issues in com bining remote sensing data from a variety of sources into a unified set of data products that can be used in the analysis of climate change. Creation of climate quality data records from remote sensing observations presents special challenges to the scien ce data processing segment of an instrument team. Throughout its history, remote sensing systems have recognized instrument calibration adjustments over time as necessary. Long -term stability over many decades is a unique climate data requirement imposed on remotely sensed data and creates special problems when information technology is rapidly evolving. Over the life of an observational data set, changes in ground processing environments, if not handled correctly, can create unexpected biases in signals and are a special challenge when the hardware, operating systems and processing libraries change on a quarterly basis. Planning for ground processing systems to support climate data records must incorporate requirements for accommodating changes to the t echnology and provide for a means of validating the stability of data products. This planning becomes particularly useful when the observational system lifetime extends through several lifetimes of the ground processing systems, and yet requires the elimi nation of errors created by changing the technologies in science data processing.

Relationship between the Clouds and the Earth's Radiant Energy System (CERES) measurements and surface temperatures of selected ocean regions

Clear sky longwave radiances and fluxes are compared with the sea surface temperatures for three oceanic regions: Atlantic, Indian, and Pacific. The Clouds and the Earths Radiant Energy System (CERES) measurements were obtained by the three thermistor bolometers: total channel which measures the radiation arising from the earth-atmosphere system between 0.3 - > 100 micrometer; the window channel which measures the radiation from 8 - 12 micrometer; and the shortwave channel which measures the reflected energy from 0.3 - < 5.0 micrometer. These instruments have demonstrated measurement precisions of approximately 0.3% on the International Temperature Scale of 1990 (ITS-90) between ground and on-orbit sensor calibrations. In this work we have used eight months of clear sky earth-nadir-view radiance data starting from January 1998 through August 1998. We have found a very strong correlation of 0.97 between the CERES window channels weekly averaged unfiltered spectral radiance values at satellite altitude (350 km) and the corresponding weekly averaged sea surface temperature (SST) data covering all the oceanic regions. Such correlation can be used in predicting the sea surface temperatures using the present CERES Terras window channel radiances at satellite altitude very easily.

Broadband measurements of lunar radiances using the Tropical Rainfall Measuring Mission (TRMM) spacecraft/Clouds and the Earth's Radiant Energy System (CERES) sensors

12 Currently, the moon is being used as a radiometric target to determine on-orbit relative shifts or shifts in the responses of certain spacecraft shortwave sensors. Along these lines, the 1998 Tropical Rainfall Measuring Mission (TRMM) Spacecraft/Clouds and the Earths Radiant Energy System (CERES) thermistor bolometer sensor observations of lunar radiances were analyzed to evaluate the feasibility using the lunar radiances to calibrate the CERES sensor responses. Over a 5 to 110 degree phase angle range, the CERES sensors were used to measure: broadband shortwave (0.3 micrometers to 5.0 micrometers ) moon-reflected solar filtered radiances; broadband total (0.3 micrometers to more than 100 micrometers ) moon- reflected solar and moon-emitted longwave filtered radiances; and narrowband window (8 micrometers to 12 micrometers ) moon- emitted longwave filtered radiances. The TRMM/CERES on-orbit radiance measurements are tied to an International Temperature Scale of 1990 (ITS-90) modeled radiometric scale at uncertainty levels approaching 0.2% (0.2 Wm-2sr-1). Therefore, the TRMM/CERES measurements should be useful in forecasting the precisions of scheduled CERES lunar measurements from the NASA Terra and Aqua Spacecraft platforms near phase angle of 22 and 55 degrees, respectively. The 7-degree phase angle, 1998 CERES shortwave, total, and window measurements yielded lunar filtered radiances of approximately 4.5+/- 0.2, 24.4+/- 0.5, and 4.5+/- 0.2 Wm-2sr-1, respectively. These lunar measurements indicate that broadband shortwave radiances can be characterized at the 5% uncertainty range. The 7-degree, shortwave lunar radiances were found to be approximately 1.5 and 3 times brighter greater the corresponding radiances found at the 22-degree and 55-degree phase angles, respectively. Therefore, the Terra and Aqua CERES lunar shortwave measurements near 22.5- degree and 55-degree phase angles should yield projected precisions in the 7% and 15% range, respectively. The CERES lunar filtered radiance are presented and discussed. Research efforts are outlined briefly for comparing the total sensor broadband and window narrowband longwave lunar radiances during the January 9, 2001 lunar eclipse.